1. Field of the Invention
The present invention relates generally to a brake booster, and more particularly to a brake booster utilizing a pump of a power steering device.
2. Description of the Prior Art
Conventionally, a valve spool is disposed within a power piston and an actuating chamber of the power piston is cut off from a drain port as a result of the movement of the valve spool in accordance with the depression force of a brake pedal. The actuating chamber of the power piston is then fluidically connected to an inlet port and the fluid flow from the inlet port to an outlet port is compressed and limited and the hydraulic fluid pressure within the actuating chamber is thereby increased. Within this system, a passage disposed upon the outer peripheral surface of the power piston is formed into an annular configuration so as to easily construct a brake booster mechanism, however, the booster will inevitably be elongated. In addition, a passage disposed upon the outer peripheral surface of the power piston may be axially formed so as to shorten the brake booster, however, it will be difficult to form the axial passage, and a groove for balancing the pressure force must be further formed due to the fact that the power piston is contacted with a cylinder wall as a result of the pressure force within the passage.
Within another type of system, a valve spool is outwardly disposed and a power piston is provided in parallel with the valve spool, the valve spool being mechanically cooperative with a brake pedal through means of a lever. Within this system, it is easy to form a passage upon the outer peripheral surface of the power piston, and in addition, the brake booster can be shortened, however, the lever, and an attaching mechanism therefor, are necessary.